1. Field of the Invention
The present invention relates to a process and an apparatus for chucking and machining an elongated cylindrical ceramic article.
1. Related Art Statement
When an elongated cylindrical article such as an engine valve-forming article is to be ground by a cylindrical grinder, it is a conventional practice that the workpiece is manually or automatically placed between a pair of chuck heads, chucked by means of a general purpose scroll chuck or opposite centers, and machined.
FIGS. 1 and 2 is a schematic view of a chucking and machining apparatus for the illustration of a conventional chucking process. According to this chucking and machining apparatus, a driving side chuck head 1 is rotatably supported by a support pole 2 at one side, and is to be rotated by a motor 3. At the other side, a rotatable tailstock 4 (driven side chuck head 4) installed at one end of a chucking pressure applicator 5. An air circuit 6 is connected to the other end of the chucking pressure applicator 5 so that a desired chucking pressure may be applied between the chucking heads 1, 4 via the chucking pressure applicator 5. The air circuit 6 is to be adjusted such that warping of the workpiece by the chucking pressure may be made smaller. The chucking pressure applicator 5 includes a cylindrical recess 5-1 formed in a support pole 7 and a piston 5-2 fitted slidably to-and-fro in the cylindrical recess 5-1 so that the chucking pressure applicator 5 may be supported and moved to-and-fro by the support pole 7. The support pole 7 is slidably and fixedly installed on a base 8 by a moving unit not shown, for example, an oil pressure device.
When a ceramic engine valve having a head diameter of 32 mm, a shaft diameter of 7.3 mm and an entire length of 109 mm as a workpiece W is to be chucked by using this chucking and machining apparatus, the workpiece W is placed between a pair of the chuck heads manually or by means of an automatic carrier, and its one end is pressed against the driving side chuck head 2 at one side (See FIGS. 1(a) and 1(b)). Then, the support pole 7 is slid in a left direction in these figures to contact the other end of the workpiece W against the driven side chuck head 5. Thereafter, the support pole 7 is fixed to the base 8 (See FIG. 1(c)). At that time, the air chuck 6 is set such that a given chucking pressure may be applied between the chuck heads 1 and 5. The driving side chuck head 1 is rotated by the motor 3, and the engine valve fixedly chucked between the chuck heads under the above chucking pressure is rotated. While the engine valve is being rotated, the surface of the engine valve is machined by a grinding tool T schematically illustrated in FIG. 1(c).
FIG. 2 is a view for illustrating a chucked state of the workpiece W in FIG. 1(c). As illustrated, frusto-conical chucking recesses 1-1, 4-1 are provided at the chucking heads 1, 4, respectively so that their conical peripheral surfaces may function as chucking faces. Beveled portions W1 and W2 are provided at an axially outer peripheral area of a large-diameter head seat portion Wa and that of a small-diameter shaft portion Wb, respectively, and are contacted with and supported by the chucking recesses 1-1 and 4-1, respectively.